Mohinder Singh Pandher and Surender Koli, the main suspects in the Nithari serial killings, were brought back from Gandhinagar in Gujarat after being subjected to narcoanalysis tests.

The duo reached Noida on Thursday morning and are being kept by the Noida police at an undisclosed location. They will be produced in a local court on Friday on the expiry of their police remand.

Police also said they are in the process of handing over documents, including the preliminary investigation report in the case, to the Central Bureau of Investigation, which began its probe into the serial killings on Wednesday after registering 19 cases.

The CBI and the forensic team are likely to visit the scene of crime on Thursday, the sources added.

Meanwhile, a bone found by a villager, became the centre of attention in Nithari village in Noida on Thursday morning.

It was found lying near a drain outside Pandher's D-5 residence. But it was not sure whether it belonged to a human being or animal.

Police had on December 29 recovered skulls and human remains from a drain behind Pandher's residence unearthing the serial killings of children and woman allegedly by him and domestic help Koli.